US 8,698,689 B2 · Assignee: Hitachi Chemical, Ltd. · Inventors: Oota; Masahiko et al.
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A multi-beam antenna suppressing an increase in loss of a Rotman lens to achieve enhanced gain. .beta.<.alpha., where: .beta. is a spatial beam-forming angle of an array antenna viewed from the a front of the antenna; and .alpha. is an angle between a center line of a Rotman lens, and a line segment connecting one of the input ports and an intersecting point S2 of the center line with a curve segment having a plurality of output ports A shape of the Rotman lens such that: .eta.=(.beta./.alpha.)(Ln/F)<1, and G is less than when .beta.=.alpha., where: F is a distance between one input port and S2; 2 Ln is an aperture length of the array antenna; and G is a size of the Rotman lens, defined as a distance between S2 and an intersecting point of the center line with a curve segment having input ports.
To begin with, a conventional antenna device using a Rotman lens will be explained with its top plan view in FIG. 8. In FIG. 8, the reference numeral denotes a Rotman lens. The reference numerals (21),(22), - - - (2m) denote respective ones of a plurality of input ports for feeding electric power, and the reference numerals (31),(32), - - - (3n) denote respective ones of a plurality of output ports for extracting electric power in the Rotman lens (1). The reference numerals (41),(42), - - - (4n) denote respective ones of a plurality of antenna elements for radiating electromagnetic waves to space, and the reference numeral denotes an array antenna having the plurality of antenna elements (41),(42), - - - (4n) arranged linearly. The reference numerals (61),(62), - - - (6n) denote respective ones of a plurality of transmission lines connecting respective ones of the output ports to respect
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What the patent claimed, word for word. All of it is now free to use.
The present invention relates to a design method for a Rotman lens usable in a multi-beam antenna device utilizable for millimeter band signal transmitting/receiving.
To begin with, a conventional antenna device using a Rotman lens will be explained with its top plan view in FIG. 8. In FIG. 8, the reference numeral
denotes a Rotman lens. The reference numerals (21),(22), - - - (2m) denote respective ones of a plurality of input ports for feeding electric power, and the reference numerals (31),(32), - - - (3n) denote respective ones of a plurality of output ports for extracting electric power in the Rotman lens (1). The reference numerals (41),(42), - - - (4n) denote respective ones of a plurality of antenna elements for radiating electromagnetic waves to space, and the reference numeral
denotes an array antenna having the plurality of antenna elements (41),(42), - - - (4n) arranged linearly. The reference numerals (61),(62), - - - (6n) denote respective ones of a plurality of transmission lines connecting respective ones of the output ports to respective ones of the antenna elements, and the reference numeral
denotes a line section comprised of the transmission lines (61),(62), - - - (6n) having different lengths. The reference numeral
denotes a center line. This antenna device is line-symmetric with respect to the center line (8). The reference numeral
denotes an auxiliary line for indicating a position of one
of the input ports. The input port
is located in a direction at an elevation angle .alpha. with respect to the center line
when viewed from S2 which is an origin of an X-Y coordinate system. The reference numeral
denotes a straight line which is indicative of a spatial beam direction upon excitation of the input port (21), and oriented in a direction at an angle .beta. with respect to a direction facing a front of the array antenna. In a primitive or basic design process, a Rotman lens is generally designed under a condition of .beta.=.alpha..
In the conventional antenna device configured as above, when one of the input ports (21),(22), - - - (2m) is excited, electric power is fed into the Rotman lens (1). The electric power in the Rotman lens
is extracted from each of the output ports (31),(32), - - - (3n), and transmitted to a corresponding one of the antenna elements (41),(42), - - - (4n) through a respective one of the transmission lines (61),(62), - - - (6n). An excitation amplitude and an excitation phase of the array antenna
are determined by which of the input ports (21),(22), - - - (2m) is excited, and the spatial beam direction is determined by the excitation phase of the array antenna (5).
In the conventional antenna device illustrated in FIG. 8, the input ports (21),(22), - - - (2m) are arranged on an arc having a radius R from a center located at a focal point S1 of the Rotman lens. The origin S2 of the X-Y coordinate system is represented by an intersecting point of the center line
with a curve segment having the output ports (31), (32), - - - , (3n) arranged thereon. S3 indicates an intersecting point of the center line
with a curve segment having the input ports (21), (22), - - - , (2m) arranged thereon. An x coordinate and a y coordinate of each of the output ports (31),(32), - - - (3n), and an electrical length w of each of the transmission lines (61),(62), - - - (6n), are expressed in the following Formulas 1 to 3, respectively: x=[2w(1-g)-b.sub.0.sup.2.eta..sup.2]/2(g-a.sub.0)
y=.eta.(1-w)
w=[-b- {square root over ((b.sup.2-4ac))}]/2a
In the above Formulas 1 to 3, g=G/F,.eta.=Ln/F,a.sub.0=cos .alpha.,b.sub.0=sin .alpha., a=1-.eta..sup.2-[(g-1)/(g-a.sub.0)].sup.2, b=2g(g-1)/(g-a.sub.0)-[(g-1)/(g-a.sub.0).sup.2]b.sub.0.sup.2.eta..sup.2+2- .eta..sup.2-2g, and c=gb.sub.0.sup.2.eta..sup.2/(g-a.sub.0)-b.sub.0.sup.4.eta..sup.4/[4(g-a.s- ub.0).sup.2]-.eta..sup.2.
Further, the radius R is expressed in the following formula: R=[(Fa.sub.0-G).sup.2+F.sup.2+b.sub.0.sup.2]/[2(G-Fa.sub.0)]
In the Formula 4, G is a size of the Rotman lens defined by a distance between S2 and S3. Further, F is a distance between the input port
and S2, and 2 Ln is an aperture length of the array antenna (5). In the basic design process, it is commonly considered that it is desirable to set approximately in the following range: 0.8<.eta.<1, i.e., set F in a range of about 1 to 1.25 times Ln, and set g to about 1.137, under a defined condition of .beta.=.alpha., in view of an advantage of being able to reduce an error in excitation phase at each of the output ports (31), (32), - - - (3n).
Patent Documents
Patent Document 1: JP 57-93701A Patent Document 2: JP 57-184305A Patent Document 3: JP 56-123105A Patent Document 4:
Problem to be Solved by the Invention
However, in the conventional antenna device illustrated in FIG. 8, as a prerequisite to allowing the line section
to be configured, the radicand inside the radical symbol in the Formula 3 is required to have a positive sign or to be zero. In other words, the following Formula 5 has to be satisfied. b.sup.2-4ac.gtoreq.0
As a prerequisite to satisfying the Formula 5, .eta.=Ln/F has to be equal to or less than 1 (.eta.=Ln/F.ltoreq.1). This means that, in cases where the aperture 2 Ln of the array antenna
becomes larger due to an increase in the number of the antenna elements (41),(42), - - - (4n), it is necessary to increase the distance F between the input port
and S2 in proportion to the aperture 2 Ln of the array antenna (5), resulting in an increase in the size G of the Rotman lens. Therefore, when the number of the antenna elements (41),(42), - - - (4n) is increased, it is necessary to increase the size G of the Rotman lens in conformity to an increasing rate of the antenna elements, which causes a problem that, even though the number of the antenna elements is increased, an appropriate gain enhancement effect cannot be obtained.
The present invention is directed to providing a low-loss multi-beam antenna device capable of, under a condition that .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of an array antenna (5); and .alpha. is an angle between a center line
and a line segment which connects one of a plurality of input ports and an intersecting point S2 of the center line
with a curve segment having a plurality of output ports (31), (32), - - - , (3n) arranged thereon, reducing G which is a size of a Rotman lens, to less than a value of G set out through a basic design process, i.e., a basic value of G when designed under a defined condition of .beta.=.alpha., and thereby suppressing an increase in loss of the Rotman lens so as to achieve enhanced gain.
Means for Solving the Problem
A multi-beam antenna of the present invention is characterized in that, under a condition that .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of an array antenna; and .alpha. is an angle between a center line (8), and a line segment which connects one of a plurality of input ports and an intersecting point S2 of the center line
with a curve segment having a plurality of output ports (31), (32), - - - , (3n) arranged thereon, a shape of a Rotman lens is set to satisfy the following relation: .eta.=(.beta./.alpha.)(Ln/F)<1 (Formula 6), and reduce G to less than a basic value of G when designed under a defined condition of .beta.=.alpha., where: F is a distance between the one input port
and S2; 2 Ln is an aperture length of the array antenna (5); and G is a size of the Rotman lens, and defined as a distance between S2 and S3 (wherein S3 is an intersecting point of the center line
with a curve segment having the input ports (21), (22), - - - , (2m) arranged thereon).
In one embodiment of the present invention, the multi-beam antenna device is further characterized in that the Rotman lens is formed using a triplate.
In one embodiment of the present invention, the multi-beam antenna device is further characterized in that the array antenna is formed using a triplate.
In one embodiment of the present invention, the multi-beam antenna device is further characterized in that each of the input ports is partially formed as two branched transmission lines to distribute and feed electric power.
In another aspect, a multi-beam antenna device of the present invention comprises: a Rotman lens having a plurality of input ports (21), (22), - - - , (2m) for feeding electric power, and a plurality of output ports (31), (32), - - - , (3n) for extracting the electric power from the input ports; an array antenna comprised of a plurality of antenna elements and adapted to radiate electromagnetic waves to space; and a plurality of transmission lines connecting respective ones of the output ports to respective ones of the antenna elements, wherein a curve for arranging the output ports thereon and a length of each of the transmission lines are set such that, when a given one of the input ports is excited, a beam is formed in a direction at an angle corresponding to that of the given input port. The multi-beam antenna device is characterized in that: .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of the array antenna when viewed from a direction facing a front of the array antenna; and .alpha. is an angle between a center line
of the Rotman lens, and a line segment which connects one of the input ports and an intersecting point S2 of the center line
with a curve segment having the output ports (31), (32), - - - , (3n) arranged thereon; and a shape of the Rotman lens is set to reduce G to less than a value of G when designed under a condition of .beta.=.alpha., where G is a size of the Rotman lens, and defined as a distance between S2 and S3 (wherein S3 is an intersecting point of the center line
with a curve segment having the input ports (21), (22), - - - , (2m) arranged thereon).
In yet another aspect, a multi-beam antenna device of the present invention comprises: a Rotman lens having a plurality of input ports (21), (22), - - - , (2m) for feeding electric power, and a plurality of output ports (31), (32), - - - , (3n) for extracting the electric power from the input ports; an array antenna comprised of a plurality of antenna elements and adapted to radiate electromagnetic waves to space; and a plurality of transmission lines connecting respective ones of the output ports to respective ones of the antenna elements, wherein a curve for arranging the output ports thereon and a length of each of the transmission lines are set such that, when a given one of the input ports is excited, a beam is formed in a direction at an angle corresponding to that of the given input port. The multi-beam antenna device is characterized in that the Rotman lens is designed according to a design procedure comprising the steps of: setting a number n of element arrays of the input or output ports; setting an arrangement pitch P of the element arrays; setting a beam number and a beam step angle; setting .beta. with respect to .alpha. to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of the array antenna when viewed from a direction facing a front of the array antenna; and .alpha. is an angle between a center line
of the Rotman lens, and a line segment which connects one of the input ports and an intersecting point S2 of the center line
with a curve segment having the output ports (31), (32), - - - , (3n) arranged thereon; calculating Fx which allows b.sup.2-4ac=0; setting a value of F; setting a value of G; and calculating respective coordinates (x, y) of the output ports of a number N corresponding to the number n of the element arrays, and a corrective line phase w in each of the output ports, whereby a shape of the Rotman lens is set to reduce G to less than a value of G when designed under a condition of .beta.=.alpha., where G is a size of the Rotman lens, and defined as a distance between S2 and S3 (wherein S3 is an intersecting point of the center line
with a curve segment having the input ports (21), (22), - - - , (2m) arranged thereon). In the multi-beam antenna device, a=1-.eta..sup.2-[(g-1)/(g-a.sub.0)].sup.2, b=2g(g-1)/(g-a.sub.0)-[(g-1)/(g-a.sub.0).sup.2]b.sub.0.sup.2.eta..sup.2+2- .eta..sup.2-2g, and c=gb.sub.0.sup.2.eta..sup.2/(g-a.sub.0)-b.sub.0.sup.4.eta..sup.4/[4(g-a.s- ub.0).sup.2].eta..sup.2, where g=G/F, .eta.=(.beta./.alpha.)(Ln/F), a.sub.0=cos .alpha., and b.sub.0=sin .alpha..
In still another aspect, an in-vehicle multi-beam antenna device of the present invention comprises: a Rotman lens having a plurality of input ports (21), (22), - - - , (2m) for feeding electric power, and a plurality of output ports (31), (32), - - - , (3n) for extracting the electric power from the input ports; an array antenna comprised of a plurality of antenna elements and each adapted to radiate electromagnetic waves to space; and a plurality of transmission lines connecting respective ones of the output ports to respective ones of the antenna elements, wherein a curve for arranging the output ports thereon and a length of each of the transmission lines are set such that, when a given one of the input ports is excited, a beam is formed in a direction at an angle corresponding to that of the given input port. The multi-beam antenna device is characterized in that .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of the array antenna when viewed from a direction facing a front of the array antenna; and .alpha. is an angle between a center line
of the Rotman lens, and a line segment which connects one of the input ports and an intersecting point S2 of the center line
with a curve segment having the output ports (31), (32), - - - , (3n) arranged thereon.
Effect of the Invention
The present invention can provide a low-loss multi-beam antenna device which is capable of, under a condition that .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of an array antenna (5); and .alpha. is an angle between a center line
and a line segment which connects one of a plurality of input ports and an intersecting point S2 of the center line
with a curve segment having a plurality of output ports (31), (32), - - - , (3n) arranged thereon, reducing G which is a size of a Rotman lens, to less than a basic value of G when designed under a defined condition of .beta.=.alpha., and thereby suppressing an increase in loss of the Rotman lens so as to achieve enhanced gain.
FIG. 1 is an explanatory diagram illustrating a configuration of a multi-beam antenna device according to the present invention.
FIG. 2 is an explanatory diagram perspectively illustrating a structure of a multi-beam antenna device according to the present invention.
FIG. 3 is an explanatory diagram illustrating a planar structure of an antenna substrate of a multi-beam antenna device according to the present invention.
FIG. 4 is an explanatory diagram illustrating a planar structure of a Rotman lens substrate of a multi-beam antenna device according to the present invention.
FIG. 5 is an explanatory diagram illustrating a power feeding system at input ports of a Rotman lens of a multi-beam antenna device according to the present invention.
FIG. 6 is an explanatory diagram illustrating directivity characteristics of a multi-beam antenna device according to the present invention.
FIG. 7 is an explanatory diagram illustrating a phase inclination in an array antenna aperture plane depending on a given input port of a multi-beam antenna device according to the present invention.
FIG. 8 is an explanatory diagram illustrating a configuration of an example of a conventional multi-beam antenna device.
FIG. 9A is an explanatory diagram illustrating a design flow for a Rotman lens in the conventional multi-beam antenna device.
FIG. 9B is an explanatory diagram illustrating a design flow for a Rotman lens in a multi-beam antenna device according to the present invention.
FIG. 10 is an explanatory diagram perspectively illustrating a part of the structure of the multi-beam antenna device according to the present invention illustrated in FIG. 2
FIG. 11 is an explanatory diagram perspectively illustrating a part of the structure of the multi-beam antenna device according to the present invention illustrated in FIG. 2
FIG. 12 is an explanatory diagram perspectively illustrating a part of the structure of the multi-beam antenna device according to the present invention illustrated in FIG. 2
First Embodiment
A multi-beam antenna according to the present invention is characterized in that, under a condition that .beta. with respect to .alpha. is set to satisfy the following relation: .beta.<.alpha., where: .beta. is a spatial beam-forming angle of an array antenna (5); and .alpha. is an elevation angle between a center line (8), and a line segment which connects one of a plurality of input ports and an intersecting point S2 of the center line
with a curve segment having a plurality of output ports (31), (32), - - - , (3n) arranged thereon, a shape of a Rotman lens is set to satisfy the Formula 6, and reduce G to less than a basic value of G when designed under a defined condition of .beta.=.alpha., where: F is a distance between the one input port
and S2; G is a size of the Rotman lens, and defined as a distance between S2 and S3; and 2 Ln is an aperture length of the array antenna (5).
Specifically, in cases where a Rotman lens is designed under the defined condition of .beta.=.alpha., as a prerequisite to satisfying the Formula 5, .eta.=Ln/F has to be equal to or less than 1 (.eta.=Ln/F.ltoreq.1). Further, it is generally considered that it is desirable to set .eta. approximately in the following range: 0.8<.eta.<1, i.e., set F in a range of about 1 to 1.25 times Ln, and set g to about 1.137, in view of an advantage of being able to reduce an error in excitation phase at each of the output ports (31), (32), - - - (3n). Thus, it is preferable to set F and G in the following respective ranges with respect to Ln: Ln<F<1.25Ln,1.137Ln<G<1.42Ln Moreover, if the aperture 2 Ln of the array antenna
becomes larger due to an increase in the number of the antenna elements (41),(42), - - - (4n), the distance F between the input port
and S2 is increased in proportion to 2 Ln, resulting in an increase in the basic value of G.
Differently, in the present invention, for example, assuming that .beta.=.alpha./2, as a prerequisite to satisfying the Formula 5, .eta.=Ln /2 F has to be equal to or less than 1 (.eta.=Ln/2F.ltoreq.1), and it is desirable to set F in a range of about 0.5 to 0.625 times Ln, and set g to about 1.137, in view of an advantage of being able to reduce an error in excitation phase at each of the output ports (31), (32), - - - (3n). Thus, desirable design can be achieved when F and G are set in the following respective ranges with respect to Ln: 0.5Ln<F<0.625Ln,0.568Ln<G<0.71Ln In this case, the Rotman lens can be designed to have a size which is 1/2 times a basic value of G when designed under the defined condition of .beta.=.alpha..
In addition, in the multi-beam antenna of the present invention which is designed based on respective coordinates (x, y) of the output ports (31), (32), - - - , (3n) and respective electrical lengths w of the transmission lines (61),(62), - - - (6n), each calculated using the Formulas 1 to 4, when electric power is fed from a given one of the input ports which has an angle .alpha. when viewed from S2, a phase inclination of a line representing respective excitation phases at the antenna elements (41),(42), - - - (4n) on the basis of that at an aperture center of the array antenna (5), as indicated by the straight line 2 in FIG. 7, is reduced by one-half as compared with the straight line 1 in FIG. 7 which represents respective excitation phases at the antenna elements (41),(42), - - - (4n) of the basic multi-beam antenna designed under the defined condition of .beta.=a, and a spatial beam-forming direction .beta. of the array antenna
is reduced to one-half of a spatial beam-forming direction .alpha. of the array antenna
in the basic multi-beam antenna designed under the defined condition of .beta.=.alpha..
Thus, in the present invention, under the condition of .beta.<.alpha., a shape of the Rotman lens is set to satisfy the relation of the Formula 6, so that it becomes possible to design a small-sized Rotman lens having a size which is .beta./.alpha. times a basic value of G when designed under the defined condition of .beta.=.alpha.. This makes it possible to suppress an increase in loss of the Rotman lens which would otherwise occur in proportion to a size thereof. In addition, even if the aperture 2 Ln of the array antenna
becomes larger due to an increase in the number of the antenna elements (41),(42), - - - (4n), and thereby the distance F between the input port
and S2 is increased in proportion to 2 Ln, a small-sized Rotman lens having a size reduced to .beta./.alpha. times the basic value of G when designed under the defined condition of .beta.<.alpha. can be designed so as to make up a multi-beam antenna device having a spatial beam-forming direction .beta. of the array antenna (5).
As shown in FIG. 2, in a multi-beam antenna device according to a first embodiment of the present invention, the Rotman lens may be formed in a triplate structure. In this case, a taper shape in complicated input and output port sections, and a phase-adjusting transmission line section (7), can be easily formed by means of etching or the like, and a first connection section
of the array antenna
and a connection port sub-section
of the transmission line section
can be electromagnetically coupled together via a first connection hole
provided in a first ground conductor (53). Further, in the multi-beam antenna device according to the first embodiment, the antenna array may also be formed in a triplate structure. In this case, it becomes possible to make up a low-loss multi-beam antenna device with a simple laminated structure of all components thereof. Specifically, the array antenna in the multi-beam antenna device according to the first embodiment is formed as a triplate-structured array antenna by laminating a slotted plate
and a feeder line
of an antenna substrate (52), and the first ground conductor
together through a dielectric (71a, 71b) interposed between adjacent ones thereof. Based on employing this structure, it becomes possible to make up a low-loss multi-beam antenna device with a simple laminated structure of all components thereof.
The above description has been made on an assumption that the present invention is applied to a commonly-used hollow parallel-plate Rotman lens, or a triplate structure in which a Rotman lens substrate
is supported by a dielectric having a low approximately equal to that of air. In a parallel plate or a triplate structure using a dielectric having a relative permittivity .di-elect cons.r, it is apparent that the Formula 6 in the present invention may be handled as the following Formula 7. .eta.=(1/ {square root over (.di-elect cons.r)})(.beta./.alpha.)(Ln/F)<1
In the multi-beam antenna device according to the first embodiment, a radiation element
formed in the antenna substrate
illustrated in FIG. 3 can radiate an electromagnetic wave having a desired frequency in cooperation with the first ground conductor
and a slot
formed in the slot plate (50), illustrated in FIG. 2, to serve as the antenna element. A plurality of the antenna elements are arranged to form the array antenna
as a whole. Further, a triplate-structured Rotman lens is made up of the first ground conductor (53), the Rotman lens substrate
and a second ground conductor (13), illustrated in FIG. 2. More specifically, as illustrated in FIG. 2, the triplate-structured Rotman lens is formed by laminating the first ground conductor (53), the transmission line section
of the Rotman lens substrate (12), and the second ground conductor
together through a dielectric (71a, 71b) interposed between adjacent ones thereof.
The first connection section
formed in the antenna substrate
is electromagnetically coupled with the connection port sub-section
of the transmission line section
formed in the Rotman lens substrate
illustrated in FIG. 4, through the first connection hole
formed in the first ground conductor (53), so that desired exciting electric power is transmitted from the output ports of the Rotman lens
to the array antenna (5).
In this process, each of a metal spacer (51a, 51b) disposed on a respective one of upper and lower sides of the antenna substrate
and a metal spacer (11a, 11b) disposed a respective one of upper and lower sides of the Rotman lens substrate
holds a respective one of the antenna substrate
and the Rotman lens substrate
in a spaced manner, while forming a metal wall around an electromagnetic coupling region between the first connection section
formed in the antenna substrate
and the connection port sub-section
of the transmission line section
formed in the Rotman lens substrate (12), so that they can contribute to efficient transmission of electric power without leakage to the surroundings, so as to achieve low-loss characteristics even at high frequencies.
In order to stably hold the antenna substrate
and the Rotman lens substrate (12), each of a void (55a, 55b) in the metal spacer (51a, 51b) and a void (14a, 14b) in the metal spacers (11a, 11a) may be filled with a dielectric (71a, 71b).
The metal spacer (11a, 11b) also forms a metal wall around the input port section
of the antenna device, so that it can contribute to efficient transmission of electric power to a high-frequency circuit through a second connection hole
formed in the second ground conductor
without leakage to the surroundings, so as to achieve low-loss characteristics even at high frequencies.
Each of the first connection hole
and the second connection hole
may be formed as a waveguide opening suited to a frequency band to be used.
In addition, based on the simple laminated structure of the components, transmission/receiving of electric power is performed by means of electromagnetic coupling, so that it is not necessary to ensure high positional accuracy during assembly at a level of conventional assembly accuracy.
Preferably, in the multi-beam antenna device according to the first embodiment, as each of the antenna substrate
and the Rotman lens substrate (12), a flexible substrate prepared by laminating a polyimide film to a copper foil is employed, wherein the radiation element (56), the feeder line (57), the first connection section (58), the Rotman lens (1), the transmission line section (7), the connection port sub-section
of the transmission line section (7), and the input port section
of the antenna device, are formed by etchingly removing an unnecessary part of the copper foil.
The flexible substrate may be prepared by employing a film as a base material and laminating a metal foil, such as a copper foil, onto the film. In this case, the radiation elements and a plurality of the feeder lines connecting therebetween may be formed by etchingly removing an unnecessary part of the copper foil (metal foil). Alternatively, the flexible substrate may be made up using a copper-cladded laminate prepared by laminating a copper foil on a thin resin sheet consisting of a glass cloth impregnated with resin. The film may be made of a material, such as polyethylene, polypropylene, polytetrafluoroethylene, ethylene fluoride-polypropylene copolymer, ethylene-tetrafluoroethylene copolymer, polyamide, polyimide, polyamide-imide, polyarylate, thermoplastic polyimide, polyetherimide, polyether ether ketone, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polysulfone, polyphenylene ether, polyphenylene sulfide, or polymethylpentene. An adhesive may be used for lamination between the film and the metal foil. In view of thermal resistance, dielectric characteristics and versatility, it is preferable to use a flexible substrate prepared by laminating a polyimide film to a copper foil. In view of dielectric characteristics, a fluorine-based film is preferably used.
As the ground conductor or the metal spacer for use in the multi-beam antenna device according to the first embodiment, a metal plate or a coated plastic plate may be used. Particularly, it is preferable to use an aluminum plate in view of an advantage of being able to produce the ground conductor or the metal spacer in a low weight and at a low cost. Alternatively, the ground conductor or the metal spacer may be made up using a flexible substrate prepared by employing a film as a base material and laminating a copper foil onto the film, or a copper-cladded laminate prepared by laminating a copper foil on a thin resin sheet consisting of a glass cloth impregnated with resin. A slot or coupling hole-forming section formed in the ground conductor may be formed by punching based on mechanical press or by etching. In view of simplicity, productivity, etc., the punching based on mechanical press is preferable.
For example, as the substrate-supporting dielectric (71a, 71b) for use in the multi-beam antenna device according to the first embodiment, it is preferable to use a foamed material having a small relative permittivity with respect to air. The foamed material may include: a polyolefin-based foamed material such as polyethylene or polypropylene; a polystyrene-based foamed material; a polyurethane-based foamed material; a polysilicone-based foamed material; and a rubber-based foamed material. Among them, a polyolefin-based foamed material is preferable, because it is lower in the relative permittivity with respect to air.
Second Embodiment
The multi-beam antenna device according to the first embodiment will be further viewed in terms of dimensions of each member, etc., and described as a second embodiment with reference to FIG. 2. Each of the slotted plate (50), the first ground conductor (53), the second ground conductor (13), the metal spacer (51a, 51b), and the metal spacer (11a, 11b), is made up using an aluminum plate having a thickness of 0.3 mm. Further, the substrate-supporting dielectric (71a, 71b) is made up using a polyethylene foam having a thickness of 0.3 mm and a relative permittivity of about 1.1. Each of the antenna substrate
and the Rotman lens substrate
is made up using a flexible substrate prepared by laminating a copper foil (having a thickness, for example, of 25 .mu.m) to a polyimide film (having a thickness, for example, of 25 .mu.m), wherein the radiation element (56), the feeder line (57), the first connection section (58), the Rotman lens (1), the transmission line section (7), the connection port sub-section
of the transmission line section (7), and the input port section (17), are formed by etchingly removing an unnecessary part of the copper foil. Each of all of the ground conductors, the slotted plate and all of the metal spacers, is made up using an aluminum plate subjected to punching based on mechanical press.
In this process, each of the radiation elements
is formed in a square shape having a side length of 1.5 mm which is about 0.38 times a free space wavelength (.lamda.o=3.95 mm) at a frequency of 76 GHz. Further, the slot
formed in the slotted plate
is formed in a square shape having a side length of 2.3 mm which is about 0.58 times the free space wavelength (.lamda.o=3.95 mm) at the desired frequency of 76 GHz, and each of the first connection hole
formed in the first ground conductor
and the second connection hole
formed in the second ground conductor
is formed as a waveguide opening having a size of 1.25 mm length.times.2.53 mm width. Twenty four antenna element arrays each made up of the radiation elements
formed in the antenna substrate
illustrated in FIG. 3, the first ground conductor
illustrated in FIG. 2, the slots
formed in the slotted plate (50), and the feeder lines (57), are arranged at a pitch of 3.0 mm which is about 0.77 times the free space wavelength (.lamda.o=3.95 mm) at the desired frequency of 76 GHz, to form an array antenna
having an antenna aperture 2 Ln of 24.times.0.77 .lamda.o as a whole. A side length is set to 2.3 mm which is about 0.58 times the free space wavelength (.lamda.o=3.95 mm) at the desired frequency of 76 GHz.
Further, the Rotman lens
having the 24 output ports to be formed in the Rotman lens substrate
illustrated in FIG. 4 is designed based on respective coordinates (x, y) of the output ports and respective electrical lengths w of the transmission lines calculated using the Formulas 1 to 4 on an assumption that F=5 .lamda.o, and G=5.7 .lamda.o, in the following range: 0.568 Ln<G<0.71 Ln, while satisfying the Formula 6 wherein .beta.=.alpha./2, i.e., a condition of .eta.=(1/2)(Ln/F)<1. Specifically, the size G of the Rotman lens
is set to a value which is about 5.7 times the free space wavelength (.lamda.o=3.95 mm) at the desired frequency of 76 GHz, i.e., to 22.5 mm.
The above members were actually laminated in order as illustrated in FIG. 2 to make up a multi-beam antenna device, and a measurement unit was connected to the multi-beam antenna device to measure characteristics thereof. As a result, a reflectance loss of each of the following eight input ports was equal to or less than--15 dB, and a gain directionality corresponding to each of the eight input ports was obtained as shown in FIG. 6. Further, it could be ascertained that a beam of the array antenna
can be formed in a direction at an angle .beta. which is about one-half of an input port angle .alpha., as shown in Table 1. In this case, an insertion loss of the Rotman lens
having the size G=22.5 mm was about 2.5 dB.
TABLE-US-00001 TABLE 1 Input Port Antenna Beam Input Port No. Angle .alpha. (degree) Angle .beta. (degree) 1 26 13.0 2 19 9.4 3 12 5.9 4 5 2.3 5 -5 -2.0 6 -12 -5.5 7 -19 -9.2 8 -26 -12.7
On the other hand, in a conventional Rotman lens designed in the following range: 1.137 Ln<G<1.42 Ln, while satisfying the condition of the Formula 5 under the defined condition of .beta.=.alpha., i.e., =Ln/F<1, it is at least necessary that G=1.137, Ln=10.5 .lamda.o, so that the size G of the conventional Rotman lens is set to a value which is about 10.5 times the free space wavelength .lamda.o=3.95 mm) at the desired frequency of 76 GHz, i.e., to 41.5 mm. In this case, an insertion loss of the Rotman lens
was about 5 dB.
As above, the multi-beam antenna device according to the second embodiment is improved in relative gain by 2.5 dB or more, in comparison on the basis of a loss in a multi-beam antenna device formed by the conventional design process, so that it can achieve excellent characteristics.
Third Embodiment
In a multi-beam antenna device according to a third embodiment, as shown in FIG. 5, a connection portion of each of a plurality of input ports (521),(522), - - - (52m) is formed as a two branched transmission lines to distribute and feed electric power, which allows the electric power fed from the input ports into a Rotman lens
to be concentrated in a central region of a plurality of output ports (531),(532), - - - (53n), so as to suppress dispersion of the electric power toward a region devoid of the output ports (531),(532), - - - (53n) in a curve segment having the output ports arranged thereon. This makes it possible to reduce an unnecessary internal reflection component to suppress deterioration in sidelobe characteristics of radiation beams of an array antenna (5). Particularly, when electric power is input from an input port, such as the input port
or the input port (52n), located at an end of the curve segment having the input ports arranged thereon, electric power may be fed while setting a phase difference between the two branched transmission lines of the connection portion. This makes it possible to control a propagation direction of the electric power fed into the Rotman lens
in such a manner as to concentrate the electric power in the central region of the output ports (531),(532), - - - (53n), to suppress deterioration in sidelobe characteristics of radiation beams of the array antenna (5). The above function never impairs the advantageous effects as shown in FIG. 6 but rather generates a synergistic effect.
(Supplementary Explanation about Objects and Effects of the Present Invention and Objects and Effects of Conventional Techniques)
As mentioned in the "Background Art", design of a lens based on the Rotman's concept is generally performed under the condition of .beta.=60. One feature of the present invention is that the present invention makes it possible to design a Rotman lens under the condition of .beta.<.alpha., using the aforementioned modified Rotman process based on the conventional Rotman lens design process. Specifically, under the condition of .beta.<.alpha., .beta. (radiation angle on the side of the antenna elements) is less than a (beam angle on the side of the Rotman lens). Thus, the present invention is effective, particularly, when it a high resolution is required with respect to a narrow angle. For example, in cases where the multi-beam antenna device according to the present invention is mounted in a vehicle, it can realize a detection capability sensitive to a range of about 15 degrees in each of rightward and leftward directions with respect to 0 degree defined by a direction perpendicular to a frontward-rearward direction of the vehicle (i.e., it has an aperture angle of up to about 30 degrees as a total of the rightward and leftward angles).
In other words, the antenna device according to the present invention can obtain ideal electric power and phase distributions required for an in-vehicle antenna device or the like.
There is a conventional technique (the Patent Document 3) where lens design is performed under a condition of .beta.>.alpha., instead of .beta.<.alpha. as in the present invention. Just to make sure, the Patent Document 3 will be mentioned below. The invention described in the Patent Document 3 is an antenna device which comprise parallel plates having a plurality of input elements adapted to be excited individually so as to feed electric power, and a plurality of output elements adapted to extract the electric power; and a transmission line for connection with an array antenna comprised of a plurality of antenna elements and adapted to radiate electromagnetic waves to space, wherein a curve for arranging the output elements thereon, and a length of the transmission line, are set based on three focal points on a curve for arranging the input elements thereon, in such a manner that, when a given one of the input elements is excited, a beam is radiated in a direction at an angle corresponding to that of the given input port, and wherein a shape of the curve for arranging the input elements thereon is not a part of a circle.
As can be understood from the above, due to the lens design performed under the condition of .beta.>.alpha. (see FIG. 2 in the Patent Document 3), the shape of the curve for arranging the input elements thereon is set so as not to become a part of a circle, which shows that this antenna device is designed based on a process totally different from the Rotman's design process.
Considering the invention described in the Patent Document 3, an application having a need to set .beta. (radiation angle on the side of the antenna elements) to be greater than a (beam angle on the side of the Rotman lens) would include a military radar operable to detect a wide angular range with a less phase error.
The description continues in the full USPTO document.
About 6,704 words. The USPTO PDF has it with every drawing.
Fees are due 3.5, 7.5 and 11.5 years after grant. This patent expired on April 15, 2026, so the fee marked "not paid" was the one that went unpaid.
MULTI-BEAM ANTENNA DEVICE
Filed Nov 2009 · published Oct 2011Multi-beam antenna device
Filed Nov 2009 · granted Apr 2014Earlier publications, parents and continuations. None of them can still be enforced, or this patent would not be listed.
Prior art cited by the examiner or applicant. Useful when you check your own idea for novelty.
Everything on this page comes from the documents linked above.
